BSA B50 -500 APG Build

[wobblywalrus]

Bradley says "... the sides of such a section should not have an included angle of more than 10 degrees at any point to the rear of maximum cross-section and the surface has to be free from defects."  Most of the drawings in the book that show a streamlined bike from overhead show a 10 degree angle on each side for a 20 degree included angle.

I did two designs.  One had a 5 degrees per side for a 10 degree included angle.  This made a very long shape with over 12 feet from nose to end of pointed tail.  I do not know the exact length.  The paper I drew the shape on was not big enough.  The other had 10 degrees per side for a 20 degree included angle.  This made a shape with a more reasonable length.  The shape was about 9 feet long from the blunt front to the pointy end and it was as wide as me in the widest part.

Next, I looked at pictures of bikes I knew were fast and had wind tunnel testing.  The Amo-Steele bikes, the 200 mph water buffalo in Australia, and several others.  The shape with a 20 degree included angle resembled the fast bikes much more closely than the shape with a 10 degree included angle.  My design uses a 20 degree maximum included angle with 10 degrees, at the most, for each side.   

[Koncretekid]

Bo,
I had read Bradley's book, and that must be where I got the 10 degree maximum. But then I searched this forum and found this response from Rex Schimmer to the thread "Bicycle Aerodynamics for those who are interested", back in 2008 in regards to a human powered bicycle called the Varna, which incidentally was clocked at 80 mph!

"Kent,
I think that I have to disagree with you regarding your thinking that the Varna would suffer from unattached air flow above 100 mph. Looking at the pictures the angle that the body converges at is certainly less that the accepted 11-14 degrees maximum also the bike has a very small surface area which minimizes skin friction which is probably the largest component of drag for the bike. There is no doubt that all of the air flow on the VARNA is attached and probably laminar, due to the low speed, so its pressure drag is only the area of the boundary layer from both sides as they converge at the tail and being pretty short and probably laminar flow the boundary layer is probably pretty thin at the rear of the bike."

I took this bit of information as an excuse to narrow up the rear of my mock-up a couple of inches -- it sure looks a lot better, and of course, looks are important .  Still less than 14 degrees, so time will tell.  I'm still trying to figure out how that CanAm 125 went 135 mph on just 22 hp.  Methinks it had to have a bit more.

Tom

[bak189]

Yep.....Can-Am 125c.c. had only 22hp.....ran 138mph......Documented facts.................all about Aero....skinny tires.....very free spinning wheels....(rear wheel when spun with chain in place would sit there and spin for 4 min.)
The little 125c.c. that Van Butler ran a SCTA events ran 136mph plus...
(his bike rear wheel with chain in place would sit there and spin forever)

I did some work on our sidecar rear wheel, trans and chain for the 2011
BUB meet.......went from 143mph to 162mph (with passenger) granted some other work also helped this increase......disc brakes make drag
drum brakes are the way to go for LSR....less drag.....every little bid helpes....especially on the small low horsepower bikes.....................

[ChrisLenahan]

I had read an article about the Can Am 125cc motor that claimed it made 32 horsepower on methonal:  http://www.snowgoer.com/output.cfm?id=2407339  The article is supposed to be from Phil Mickleson who it appears has that engine on display at his home in Duluth.  See here also: http://www.canned-ham.com/index.php/history/setting-the-land-speed-record/  BAK, I'm not trying to contradict you just showing what I've read and looking for clarification.  The 32 hp figure may be a calculated at the crank figure or something.  And BAK, I don't expect 115 to be easy for a beginner at Bonneville like me,  the motor has the capability I'm sure but tuning it to get there is another story.

[Koncretekid]

Great information on the CanAm.  But it also raises the question:  was this motor really a motorcycle motor? I was not aware that Can Am actually made a water cooled motorcycle at that time. The BUB rules state the following: "Modified class can include factory produced off road, limited production and road racing motorcycles with less than 500 in production. This class does not include factory produced road racing or any other specialized racing models unless available to the public." SCTA rules are similar. 

The 32  hp rating sounds more reasonable for the speed they attained.  So if I use the same fairing, with a few modifications and 43 hp, how fast should I go?  I know my wheels won't spin for 4 minutes (lots of drag in the BSA transmission) but what other drag will I have that they didn't?  I expect to use some cooling holes, but not very large.  It will be fun to find out

Tom.

[ChrisLenahan]

It was based on a production Can Am model but used a cylinder assembly that was a prototype I guess and a special crank. By the way 61mm later became the standard stroke for the Can Am/ATK/SWM 250cc motors.  The frame and engine cases were production based, but as Rotax and Can Am were and are part of the same company they worked very together and the technology developed in this project later found its way into many other Rotax products including snowmobiles, watercraft, aircraft engines, kart engines and even motorcycle engines.  The 250cc twin rotax roadrace engine used a similar port design to the record bike from what I've been able to learn.

[wobblywalrus]

Some better answers to your earlier questions.

Which is best, leaving the fairing back open versus closed.  Engines need a lot of airflow to keep cool, and also, cooler air at the carb intakes helps power.  I leave the back open.  It is a passage for hot air escape.

Is a belly pan extending back around the rear wheel helpful?  Nothing I have read and nobody I have talked to has say it is a bad idea.  In theory the undercarriage is a rough non-aerodynamically shaped area and it would benefit by streamlining.  Eventually the Triumph will have a long belly pan.

Should the edges between the pan and upper body be hard or soft?  Soft, probably.

Keep in mind that the best way to answer these questions is to test the bike with different configurations in the wind tunnel.

Tom Mellor's silver Triumph partial streamliner is a good example to look at.  He pays a lot of attention to detail.  It has raced at BUB for many years and there are a lot of good photos on Ray the Rat's "Chevy Asylum."   

[Jon]

The MotoGP bikes put a fair bit of effort into taking the bellypan back around the rear wheel.
Guessing they would put a fair bit of aero work into it.

Cheers
jon

[bak189]

In regards to the record setting Can-Am engine that Phil has in his parlor.......................................................................................
From Bob Barker  "Last time I saw the engine it was in a MX bike in Valcourt, Canada.  It siezed up as soon as they revved it up. Could be the engine out of Woody Leone's machine.  Woody set several records and his bike looked exactly like mine.  31 H.P. that is on Alky"

[bak189]

In addition regarding the question about a belly pan to and around the rear wheel............From Bob Barker: "Had to look at some of the pics.
Yes it did, the whole rear section was a pretty simple alum. sheet forming...lots of pop rivits.  We reduced the Cd drag from .608 with the backbone frame, down to .372 with the cut-down "low boy" frame.  It was so slippery that I coasted for 3 miles back to impound after the motor siezed-up at 138mph." .....for inquiring minds.... right from the man........................

PS. Engine stuck-up on the return run.......................................

[saltwheels262]

 the motor siezed-up at 138mph."

Engine stuck-up on the return run.......................................

was there a record set on the run ?

[Koncretekid]

Wobbly (Bo),
Thanks for your response.  That is why we pose questions here.  I know the answers are already out there and although I love the innovation process,  I really don't want to re-invent the wheel.  As for Tom Mellor's Triumph,  his bike had probably the biggest influence on my build.  I met Tom the year after he set the 185 mph record, and a photo of his bike has always been pinned above my work bench.  There's a good article about his bike at: http://www.motorcycleclassics.com/classic-british-motorcycles/tom-mellor-1969-triumph-trident-T150.aspx

BAK (Bob),
You mentioned that Bob Barker answered your questions after studying photographs.  Has he got any that he can share with us?  The only ones I've seen are on the Airtech website, and a couple in Bradley's book on how to build a motorcycle.  I'm sure there would be several people here that would love to see them.

Tom

[bak189]

Yes, a record was set on that return run....average of 136mph, that record still stands on the AMA books......the SCTA record was upped by the supper fast 125c.c. of the Van Butler Team

Back in the 1970's the motorcycle part of SCTA racing had AMA sanction
so records set at that time were both SCTA and AMA records...............
AMA sanction and records are now part of the anual all motorcycle BUB Speed Trials.................................................................................

[Koncretekid]

Doug has got a start on my fairing for 2012, but we have an important question.  Regarding the so-called seat/tail section "no part of the seat/tail section may be closer than 4" from the ground..."  This is from the 2009 rulebook, as I do not have access to any newer version.  The question is, where does the 4" measurement start?  My belly pan is only 1-1/2" inches from the ground, and we would like to make this continue to the back of the seat/tail section, but where must it be 4" from the ground?  At the rear extremity, or at the rear axle, or where?  I will repost this in the SCTA rule questions as well.

The bike is now draped with a single layer of vinyl ester fiberglass cloth, which will be thickened up as soon as we can establish the correct belly pan.  Now if I could just figure out how to get into it!

Tom

[55chevr]

Tom - Looks like you will have to crawl in from underneath to see through the steering head.   Nice work ...